docs: def get_thin_rect_vertices(ox, oy, dx, dy, r):
      """Given the starting point, ending point, and width, return a list of
      vertex coordinates at the corners of the line segment
      (really a thin rectangle).
  
      """
      if ox < dx:
          leftx = ox
          rightx = dx
          xco = 1
      elif ox > dx:
          leftx = ox * -1
          rightx = dx * -1
          xco = -1
      else:
          return [
              ox - r, oy,
              ox + r, oy,
              ox + r, dy,
              ox - r, dy
          ]
      if oy < dy:
          boty = oy
          topy = dy
          yco = 1
      elif oy > dy:
          boty = oy * -1
          topy = dy * -1
          yco = -1
      else:
          return [
              ox, oy - r,
              dx, oy - r,
              dx, oy + r,
              ox, oy + r
          ]
  
      rise = topy - boty
      run = rightx - leftx
      theta = atan(rise/run)
      theta_prime = ninety - theta
      xoff = cos(theta_prime) * r
      yoff = sin(theta_prime) * r
      x1 = leftx + xoff
      y1 = boty - yoff
      x2 = rightx + xoff
      y2 = topy - yoff
      x3 = rightx - xoff
      y3 = topy + yoff
      x4 = leftx - xoff
      y4 = boty + yoff
      return [
          x1 * xco, y1 * yco,
          x2 * xco, y2 * yco,
          x3 * xco, y3 * yco,
          x4 * xco, y4 * yco
      ]